Extrusion heads of this kind are known in various forms. They are found in such extrusion apparatus as extrude profile strips in which portions of different materials are arranged next to one another. Often, in such extrusion apparatus, the screw extruders are arranged pickaback over one another but they can also be arranged along side one another. With known extrusion installations of this kind, the extruder head consists of a part fast to the extruder which usually has in the middle a projection block at an acute angle to the extrusion direction whose edges,running at acute angles to one another, are aimed in the extrusion direction and enclose between them the flow channel. The movable parts are closed against this central projection and are locked here during extrusion by clamps which are pushed by hydraulic cylinders. For opening these movable parts, special hydraulic cylinders are provided. While with extrusion installations of this kind with two screw extruders, a central fixed projection and two hinged movable parts are provided, installations with more screw extruders are thereby expanded that, for example, between a movable body part and the fixed central body part an additional plate is arranged.
An objection of all of these extrusion installations is that the way from the tip of the extruder screw to the extrusion die is long and the flow channels are located in different division planes. With these long passages, a considerable amount of material is lost which must be removed out of the flow channels in the cleaning of the extrusion installation after the extrusion process and cannot further be used. In particular with the main extruder of an extruder installation of this kind, considerable material is lost. Of particular disadvantage is that the head through the long flow channels has a high flow resistance which results in high mass temperatures and/or limited output.
A further disadvantage is that the opening process with the removal and two-sided opening of the clamps and the subsequent opening of the movable parts requires a considerable amount of time which results in losing production time when there is a change-over from one material combination to another material combination for the extrusion process. Special closing and locking by means of the clamps which must be swung and then actuated by hydraulic cylinders after the cleaning process, takes away a considerable amount of production time.
The known extrusion heads of this kind are also not easily produced. The high pressures working against large surfaces require a very robust construction of the main parts of the extrusion head. On the other hand, these main parts, in particular in the different separation planes, must be machined with great accuracy so that the three or more parts close tightly with one another.